Polyfluorene Copolymer with a Multiply Blocked Rotaxane Architecture in the Main Chain: Synthesis and Characterization

To improve the physical properties of polymer materials, a novel copolymer with a multiply blocked rotaxane architecture in the main chain was synthesized through Suzuki dehalogenative polycondensation from a 2,7-dibromofluorene/gamma-cyclodextrin (gamma-CD) inclusion complex and 9,9-dioctylfluorene-2,7-trimethylene diborate in the presence of a tetrakis(triphenylphosphine)palladium(0) catalyst. As demonstrated by computational calculations, the dioctyl groups were large enough to prevent the dethreading of gamma-CD molecules. A copolymer polyrotaxane with a gamma-CD/structural unit ratio as high as 1/1.4 and a bimodal molecular weight distribution was obtained, as proved by its H-1-NMR spectrum and size exclusion chromatography curve, respectively. The polyrotaxane showed lower thermal stability and higher solubility in polar solvents in comparison with the noncomplexed homologue. The fluorescence spectra of both the complexed and noncomplexed copolymers exhibited typical well-resolved blue emission bands that arose from the fluorene chromophore units. In dimethylformamide solutions, the ratio of the intensities of the peaks of the emission spectra (emission spectra intensities(413) for the 0-0 band and emission spectra intensities(437) for the 0-1 band) was higher for the polyrotaxane than the noncomplexed copolymer, and this demonstrated a reduced quenching effect of the environment induced by the protection of the polymer chain by the macrocycle. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110:2384-2392, 2008